Re: "interval hour to minute" or "interval day to minute"

Noah Misch wrote:
> On Sun, Apr 17, 2011 at 04:55:51PM +0100, Jack Douglas wrote:
> > I discovered the 'fields' option of 'interval', but i can't figure out
> > from the docs how it is supposed to work. Are "hour to minute" and "day
> > to minute" really the same thing? And if not, in what circumstances are
> > they treated differently?
>
> As of version 8.4, they behave identically. The code has this comment, some
> form of which probably belongs in the documentation:
>
> /*
> * Our interpretation of intervals with a limited set of fields is
> * that fields to the right of the last one specified are zeroed out,
> * but those to the left of it remain valid. Thus for example there
> * is no operational difference between INTERVAL YEAR TO MONTH and
> * INTERVAL MONTH. In some cases we could meaningfully enforce that
> * higher-order fields are zero; for example INTERVAL DAY could reject
> * nonzero "month" field. However that seems a bit pointless when we
> * can't do it consistently. (We cannot enforce a range limit on the
> * highest expected field, since we do not have any equivalent of
> * SQL's <interval leading field precision>.)
> *
> * Note: before PG 8.4 we interpreted a limited set of fields as
> * actually causing a "modulo" operation on a given value, potentially
> * losing high-order as well as low-order information. But there is
> * no support for such behavior in the standard, and it seems fairly
> * undesirable on data consistency grounds anyway. Now we only
> * perform truncation or rounding of low-order fields.
> */

I am lost on how we could mention that in the docs.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +